Update ex_arma2.py

Correcting type, and leaving maparams and arparams around for later comparison.

https://github.com/statsmodels/statsmodels/issues/1116#issuecomment-26216044
Update gettingstarted.rst

correcting typo
Merge pull request #1117 from jsphon/patch-1

DOC: Update ex_arma2.py